In the long term evolution (LTE) system and in the research of the machine type communication (MTC) technology, for low-cost and low-throughput type user equipment, a research topic of the narrow band-Internet of Things (NB-IoT) is proposed, that is, a low-throughput wireless communication service is provided for NB-IoT low-cost user equipment (UE) in a frequency band of 200 kHz. A dedicated core network may be configured for users with the Narrow Band-Cellular Internet of Things (NB-CIOT) technology. An operator may manage these special-purpose UEs in the dedicated core network so as to distinguish them from ordinary users to minimize the impact on ordinary users. At the same time, the NB-IoT introduces different uplink narrowband access capabilities and optimized data transmission solutions for characteristics of the UE, i.e., low cost and small data amounts for transmission. The optimized data transmission solution includes optimization solutions based on user plane and control plane transmission. For smartphone users, the optimization solutions based on user plane and control plane transmission may also be extended.
In the optimization solution based on user plane transmission, similar to the LTE process, data is transmitted through a data radio bearer (DRB), and signaling is still transmitted through an SRB1/SRB2, where the SRB is a signaling radio bearer. The current standard has specified that only one DRB is configured for the NB-IoT user. Smartphone users that support the user plane solution may support multiple bearers. The network side introduces suspend and resume processes. The base station and the mobility management entity (MME) store user text information in the suspend process and may rapidly activate a user text in the resume process, and the suspend and resume of S1 interfaces are initiated by the base station. After the air interface suspend process is completed, the UE is switched to the idle state. When the UE needs to transmit data or “signaling+data” in the idle state, the UE may directly use the resume mechanism without performing the process of air interface encryption. The user text information includes the user identifier (ID) information, ID information related to the S1 interface user, information related to the user security, the bearer information, and information related to the service quality. The user historical information includes the historical information of the user in the connected state, and the historical information of the user which is reported by the UE and recently resided in the connected state and the idle state. When the user moves to the target base station in the suspend state, and when the target base station initiates the resume process, the target base station may obtain user text information from the source base station that stores the user text information through the X2 interface or the S1 interface. After the air interface resume process is completed, the UE is switched to the connected state. The radio access network (RAN) and the core network are aware of a state transition of the UE.
Meanwhile, with the continuous evolution of wireless communication technologies and protocol standards, the mobile packet traffic has been developed tremendously, and the data throughput capability of single UE has been continuously improved. In the LTE system, as an example, data transmission at a maximum downlink rate of 100 Mbps may be supported in a 20 M bandwidth. In the subsequent enhanced LTE system and the subsequent 5G system, the data transmission rate will be further increased, even up to tens of Gbps. The 5G technology features: seamless wide-area coverage, large-capacity hotspots, large number of connections with low power consumption, high reliability with low latency, and the like. One goal of the design for the next-generation RAN at the release 14 of the 3rd Generation Partnership Project (3GPP) is to use a single technology architecture to support multiple types of traffics, such as enhanced mobile broadband (eMBB), massive machine type communications (mMTC), ultra reliable and low latency communications (URLLC), and the like. In order to achieve the above goal, the design of the user plane architecture in the 5G New Radio (NR) needs to be flexible enough. In recent years, deployment of the centralized, cooperative, cloud & clean-radio access network (C-RAN) of the baseband Unit (BBU) and the radio remote unit (RRU) has been more and more widely used in many countries and regions around the world. In order to shield the underlying diversified access technology and support the traffic-oriented access, the 5G access network has a two-level network function architecture with the wireless center unit (CU) and the wireless distributed unit (DU) included, similar to the architecture of BBU+RRU in LTE. If the CU and the DU are deployed in the same network device, a distributed network architecture is provided, as shown in FIG. 1. If the CU and the DU are deployed in different network devices, a centralized network architecture is provided, as shown in FIG. 2. The CU satisfies the user-centered design concept, assumes the centralized control and management functions of the wireless network, and may serve as a service anchor for the UE. The DU is a remote access unit and includes a radio frequency function and a partial processing function. The interface between the CU and the DU may be called fronthaul, and the specific position division of the fronthaul (that is, the position at which the division is performed on the user plane) is currently being standardized. For simple description, the interface between the 5G RAN and the 5G CN is referred to as NG1 interface, and the interface between 5G RANs is referred to as NG2 interface.
In order to meet energy-saving requirements of the user and reduce the signaling interaction between the CN and the RAN, an inactive mode in the control of the RAN is considered to be introduced, the RAN side triggers the UE to enter this mode, and the UE may move in this mode without data transmission, and may process paging messages. When downlink data arrives at the base station or when the UE has uplink data to be transmitted, the UE may be triggered to initiate an air interface resume process and is switched to the connected state. The CN is unaware of the inactive state, in the control of the RAN, of the UE.